Development of 9 wt.% Cr steels for next generation power plant

There is a need to increase the thermal efficiency of coal fired power plants. High chromium ferritic steels have historically been used to manufacture steam pipes, tube and headers. Over the last forty years there has been a continuous development of the 9 – 12 wt. % chromium martensitic alloys which has allowed the service temperature to be increased from 510°C – 550°C1. There is now a high demand for Ultra Super Critical coal fired power plants which operate at 650°C and hence have an increased thermal efficiency. The aim of this research project was to develop a MarBN steel (Martensitic Steel Strengthened with Boron and Nitrides) with an optimised composition in order to allow MarBN to be used at 650°C. In order for MarBN to be used within high temperature applications it is vital to understand how microstructural changes can have an impact on their creep strength. This is a key area that the present research has focused upon. The long term creep strength of 9 wt. % chromium ferritic steels is derived from the stability of the microstructure over its service life, which has a direct relationship to the stability of the precipitates and the lath structure within the microstructure.